The present invention relates to a semiconductor package and fabricating method, and more particularly, to a semiconductor package and fabricating method thereof which improves operational reliability by preventing air bubbles from being trapped at both sides of a polyimide tape used in a lead on chip (LOC) method to mount a semiconductor chip on inner leads and bus bars of a lead frame having no die pad.
In general, a semiconductor package is called a hermetic sealing instrument of semiconductor chips such as transistors, diodes, and integrated circuit (IC). Semiconductor chips are hermetically sealed since their operational characteristics are degraded when humidity or dust adheres to or otherwise contaminates their surface. Also, a semiconductor chip, such as a planar type transistor which has a stabilized surface can be molded not by hermetic sealing but by an epoxy polyimide tape. And, even in that case, it is called a semiconductor package. The semiconductor package protects not only the surface of the semiconductor chip from external humidity or dust but also the semiconductor chip and slender leads extending therefrom damaging external forces. In power semiconducotr devices, the semiconductor packages are ideally designed to effectively emit heat generated at a junction. On the other hand, in diffusion transistors, such as mesa and planar type transistors, the semiconductor chip itself becomes the collector.
In a conventional LOC semiconductor package, as shown in FIG. 1, a lead frame 10 without a die pad is used. Leads 12 have inner leads 14 and outer leads 16. Bus bars 18 extend from corners of the lead frame 10.
Referring to FIGS. 2-4, a tape bonding process of the LOC semiconductor package using the conventional lead frame 10 of FIG. 1 is now described in detail.
First, as shown in FIG. 3, an adhesively double-faced die-bonding polyimide tape 30 is arranged under the inner leads 14 and bus bars 18 shown in FIG. 1. The polyimide tape 30 is cut to form cut tape portions 32, each of which is fitted to the size of the inner leads 14 and the bus bars 18 by a tape cutter 20 which has a rectangular-type blade 24 protruding from a cutter body 22 as shown in FIGS. 2A and 2B. The tape portions 32 are then adhesively bonded to the inner leads 14 and bus bars 18. At that time, as shown in FIG. 4, a heater block 42 installed over the lead frame 10 bonds the polyimide tape 30 completely by heating. The process is progressed with winding the polyimide tape 30 from the first reel 44 to the second reel 46. After the bonding process, a piercing hole is formed at the center of the tape wound at the second reel 46, as shown in FIG. 3. Next, the semiconductor chip (not shown) is bonded to the tape 30 at the back side of the inner lead 14 and the bus bars 18, followed by wire-bonding and molding. At that time, the semiconductor chip has bonding pads at its center.
In the above conventional LOC package and fabricating process thereof, when the tape is bonded with the inner leads and the bus bars, air does not flow out. Also, during bonding process of the semiconductor chip and the tape, air remains underneath the tape and forms an air bubble, because there is no outflow path of air. The air between the edge of the semiconductor chip and the tape flows out but the air between the center of the tape and the semiconductor chip remains because the outflow speed of air is slower than the bonding speed. The air bubble becomes the source of shorting problem in wire bonding process and damages the package body in molding process, degrading the reliability of the semiconductor package.